1. Field of the Invention
This invention relates generally to a data communication apparatus for data communication with other stations via a telephone. More particularly, it relates to a data communication apparatus that is capable of switching to talking by an attached telephone set.
2. Description of the Related Art
The recent remarkable spread of computers is greatly influencing our community. The essential advantage of the computer to process a large volume of data rapidly and precisely contributes greatly to this. However, one of the greatest significance of the computer in modern society lies in the application thereof to terminals in a communication network established all over the country or world.
At present, the public telephone line is one of the most simple and widely used communication networks. The computer can function as a data communication apparatus that is actually capable of communication on a country wide basis.
FIG. 1 is a block diagram showing a configuration of the above-mentioned conventional data communication apparatus. FIG. 1 shows a structure including the computer within the data communication apparatus. In practice, a partial function of an existing computer is often utilized as the data communication apparatus.
There are some cases where not only computers but also word processors are employed as a data communication apparatus by incorporating a card-type modem and using a CPU (Central Processing Unit) as a control device.
Referring to FIG. 1, the data communication apparatus includes a line connection unit 16 connected to a public telephone line via terminals 12 and 14 for connecting and disconnecting the data communication apparatus with the public telephone line; a modem unit 18 connected to line connection unit 16 for data transmission/reception with another station and for the management of accompanying communication procedures by being line-connected to another station via line connection unit 16; and a computer 20 connected to modem unit 18 for managing data transmitted/received between another station and the overall communication. The public telephone line has an attached telephone set 22 provided in parallel with line connection unit 16.
The line connection unit 16 includes a line transformer 24 having the primary coil connected to modem unit 18 and the secondary coil connected to terminals 12 and 14 of the public telephone line contact to couple the circuits of the modem unit 18 side and the circuits of the public telephone line side by magnetic coupling for transmitting signals; a switch SW2 provided between line transformer 24 and terminal 12 to switch between a connected position and a disconnected position of the line transformer 24 and terminal 12 controlled by modem unit 18; a transmitter amplifier 28 having the input connected to modem unit 18 and the output connected to line transformer 24 for amplifying the signal from modem unit 18 to be transmitted; and a receiver amplifier 30 having the input connected to line transformer 24 and the output connected to modem unit 18 for amplifying the received signal from the public telephone line via line transformer 24 to be applied to modem unit 18.
The modem unit 18 includes a modem 32 connected to line connection unit 16 for modulating the data to be transmitted to an analog signal from a digital signal, and demodulating received data to a digital signal from an analog signal; a modem controller 34 connected between modem 32 and a computer 20 for monitoring the communication status while executing communication procedures with another station by modem 32, and exchanging data and communication information with computer 20 for detecting the termination of the communication or an accidental condition of the communication status to generate a termination command; and a relay circuit 36 operative in response to a termination command for disconnecting switch SW2. The relay circuit 36 includes a relay 38 having one end connected to the power potential Vc for operating switch SW2. It further includes a transistor 40 having the base connected to modem controller 34, the collector connected to the other end of relay 38, and the emitter connected to the ground potential, respectively.
The computer 20 includes a CPU 42 connected to modem controller 34 and other peripheral equipment via an shown interface (not shown) for executing a program that controls data transmission/reception; a keyboard 44 connected to CPU 42 for the operator to provide instructions to CPU 42 thereby; a display 46 connected to CPU 42 for displaying the message of CPU 42; a timer 48 connected to CPU 42 to be used by CPU 42 for managing its own operation and the operation of the peripheral equipments; a ROM (Read Only Memory) 50 connected to CPU 42 having information not requiring dynamic rewritting; a RAM (Random Access Memory) 52 for CPU 42 to use as a working storage; and a disk 54 wherein the data to be transmitted/received and the overall data including the program are written in. A flexible disk and the like may be used instead of disk 54.
The attached telephone set 22 is used to achieve line connection manually by the operator, as well as being utilized for talking. The attached telephone set 22 includes a switch SW1 which is turned on by the operator lifting the telephone handset, not shown (off hook).
Referring to FIG. 1, the operation of a conventional data communication apparatus will be described. There are two ways of line connection. The first connection method is a manual calling by the operator using the attached telephone set 22. The operator lifts the telephone handset of the attached telephone set 22. This turns switch SW1 on. The operator dials the telephone number of the destination station to establish line connection with the destination station. This manner is similar to that of a general telephone set.
The second connection method is to utilize the automatic dialing function of modem unit 18. The telephone number of the destination station is previously stored in modem controller 34. When modem controller 34 is instructed by the operator to establish line connection with a predetermined station, it will send current intermittently to the base of transistor 40 in accordance with the telephone number of the destination station. The intermittent conductance of transistor 40 will operate relay 38 to turn switch SW2 on/off intermittently. This causes information required for the connection with another station to be sent as dialing pulses to the exchange device of the public line for establishing line connection with the destination station through a predetermined procedure. The destination telephone number is not necessarily stored in modem controller 34. In another method, it is stored in computer 20, where modem controller 34 is instructed by computer 20.
In the case of manual line connection, the operator will operate the modem controller 34 to turn SW2 on after confirming the line connection. In the case of line connection by the modem, switch SW2 is turned on after the dialing pulses are sent. A program for the execution of data communication is previously loaded in RAM 52. CPU 42 will pass the data stored in disk 54 to modem unit 18, as well as receive data from modem unit 18 for writing the same into a file in disk 54, in accordance with the program for data communication. In this event, information regarding the communication status is exchanged between CPU 42 and modem unit 18, when necessary.
The modem controller 34 is provided to perform error control with respect to communication and other necessary procedures without the imposition on CPU 42. For the transmission of data, modem controller 34 receives data to be transmitted from CPU 42 and controls modem 32 to demodulate and transmit the data, as well as notifying CPU 42 of the information of the transmission result. For the reception of the data, modem controller 34 receives the demodulated data from modem 32 and information of the reception result to notify CPU 42.
Furthermore, the modem controller 34 turns switch SW2 off by operating relay circuit 36 for the termination of line connection when an unrecoverable error is detected. The modem controller 34 will also turn switch SW2 off when transmission/reception of all data is completed.
Talking by the attached telephone set 22 is possible when switch SW1 is on, while data communication is possible when switch SW2 is on. If switch SW1 is on during data communication, noise will be carried to the telephone line from the telephone handset, leading to the possibility of malfunction of modem 32. Therefore, it is necessary to place the telephone handset on its hook during data communication to keep switch SW1 off. All such switching operation is carried out by the operator in general.
When transmission/reception of the data is completed, or when communication error occurs, switch SW2 is turned off by modem controller 34. As described above, switch SW1 is off during communication. Consequently, as switches SW2 and SW1 are both in the off position, the line is disconnected. The line will also be disconnected when the destination station encounters a likewise state.
With the apparatus shown in FIG. 1, it is difficult for the operator to interrupt the data communication and commence talking with another station using the attached telephone set. The data communication apparatus shown in FIG. 2 is designed to deal with this problem. The difference between the data communication apparatus of FIG. 2 and that of FIG. 1 is that a switch SW3 is provided in series with switch SW1 in the connection circuit of the attached telephone set 22, and that the apparatus further includes an off hook detecting circuit 58 for detecting the off hook state of the telephone handset of the attached telephone set 22 to provide an off hook detection signal to modem controller 34 via connection line 64. Further, a relay circuit 60 is connected to modem controller 34 by connection line 62 for operating switch SW3 responsive to the operator's talking request instruction and communication commence instruction. In FIG. 2, the elements identical or corresponding to the elements in the data communication apparatus of FIG. 1 are given identical names and numbers. The functions thereof are also identical. Therefore, the detail descriptions thereof will not be repeated here.
FIG. 3 is a more detailed block diagram of a portion of FIG. 2. Referring to FIG. 3, the off hook detection circuit 58 includes a bidirectional photo coupler 66 having one input connected to switch SW3, the other connected to terminal 14, one output connected to the power potential Vc and the other connected to modem controller 34 via connection line 64, and also grounded via a resistor R. The relay circuit 60 includes a relay 68 having one end connected to the power potential Vc for disconnecting switch SW3, and a transistor 70 having the base connected to connection line 62, the emitter connected to the ground potential, and the collector connected to the other end of relay 68. In FIG. 2, the telephone set is connected to terminals 73 and 75.
Referring to FIGS. 2 and 3, the conventional data communication apparatus operates as follows. Prior to data communication, the operator lifts the telephone handset of the attached telephone. The photo coupler 66 is conductive and the potential of connection line 64 rises. The modem controller 34 will turn switch SW2 off in response to the rise of this potential.
After line connection by the attached telephone, the operator will operate the communication switching button (not shown) of modem controller 34 to send an attached telephone disconnection signal to connection line 62. The relay 68 is operative to the conduction of transistor 70 to turn switch SW3 off. Simultaneously, the modem controller 34 operates relay circuit 36 so that switch SW2 it turned on.
In accordance with the above operation, modem unit 18 is line connected with another station through line connection unit 16 to execute transmission/reception of data.
In the case the operator wants to talk with the destination station during data transmission/reception, the operator will lift the telephone handset of the attached telephone set and push a talking request button, not shown, of modem controller 34. The modem controller 34 will raise the potential of connection line 62 in response to this operation. Due to the conduction of transistor 70, relay 68 operates to turn switch SW3 on, and talking will be possible. Simultaneously, the modem controller 34 operates relay circuit 36 to turn switch SW2 off. Data communication will recommence by pressing the communication switching button again.
The communication switching button and the talking request button may be provided at the input terminal of modem controller 34. Also by allocating functions to arbitrary keys in the keyboard 44 with a program executed in CPU 42, the selected key may be notified to modem controller 34 from CPU 42.
The following problems are seen in the conventional apparatus.
The conventional data communication apparatus shown in FIG. 1 is relatively simple. However, the timing of the switching operation between talking and data communication is so difficult that the inconvenience of line disconnection often occurs. This is seen when both switches SW1 and SW2 are turned on by mistake. Also in the event when both switches SW1 and SW2 are turned on by mistake, there is the possibility of noise entering modem unit 18 from the attached telephone set to cause communication error. When such line disconnection occurs, it will be necessary to reconnect the lines. Accordingly, the operation efficiency of this conventional data communication apparatus is low.
The switching between data communication and talking with the apparatus shown in FIGS. 2 and 3 is carried out by the hardware so disconnection by operation error seldom happens. However, there is the necessity of newly providing a relay circuit 60, an off hook detecting circuit 58, etc. to the circuit for connection of the attached telephone set. For this reason, data communication apparatus will become large-sized and the cost will rise. There is also the need to discriminate the circuit for the connection of the attached telephone set from the circuit for the connection of the public telephone line, leading to difficulty in operability.
Thus, a data communication apparatus with reliable operability having a suitable balance between a simple and not expensive structure, and a structure with minimum possibility of operation error is desired.